ErrorHandlerTest: restore_error_handler() on assertion failure
minor #9742 ErrorHandlerTest: restore_error_handler() on assertion failure (nicolas-grekas)

This PR was submitted for the 2.4-dev branch but it was merged into the 2.4 branch instead (closes #9742).

Discussion
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ErrorHandlerTest: restore_error_handler() on assertion failure

Before the patch, if any test fail in src/Symfony/Component/Debug/Tests/ErrorHandlerTest.php,
phpunit's error handler is not correctly restored.
When running a test batch, this breaks other tests that rely on its behavior (@expectedException PHPUnit_Framework_Error)

Commits
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a6ed37c ErrorHandlerTest: restore_error_handler() on assertion failure